1FEATURES
2• Low Voltage Supply (3V–5.5V)
• 22 mA Output Drive Current
• No RFI Radiation
• Adaptable to All Injector Current Levels
• Highly Accurate Operation
• TTL/CMOS Compatible Input Logic Levels
• Short Circuit Protection
• High Impedance Input
• Externally Set Holding Current, IH
• Internally Set Peak Current (4 × IH)
• Externally Set Time-Out
• Can be Modified for Full Switching Operation
• Available in Plastic 8-Pin PDIP

APPLICATIONS
• Fuel Injection
• Throttle Body Injection
• Solenoid Controls
• Air and Fluid Valves
• DC Motor Drives

DESCRIPTION
The LM1949 linear integrated circuit serves as an
excellent control of fuel injector drive circuitry in
modern automotive systems. The IC is designed to
control an external power NPN Darlington transistor
that drives the high current injector solenoid. The
current required to open a solenoid is several times greater than the current necessary to merely hold it
open; therefore, the LM1949, by directly sensing the
actual solenoid current, initially saturates the driver
until the “peak” injector current is four times that of
the idle or “holding” current (Figure 19–Figure 22).
This guarantees opening of the injector. The current
is then automatically reduced to the sufficient holding
level for the duration of the input pulse. In this way,
the total power consumed by the system is
dramatically reduced. Also, a higher degree of
correlation of fuel to the input voltage pulse (or duty
cycle) is achieved, since opening and closing delays
of the solenoid will be reduced.
Normally powered from a 5V ± 10% supply, the IC is
typically operable over the entire temperature range
(−55°C to +125°C ambient) with supplies as low as 3
volts. This is particularly useful under “cold crank”
conditions when the battery voltage may drop low
enough to deregulate the 5-volt power supply.
The LM1949 is available in the plastic PDIP, (contact
factory for other package options).